1. Field of the Invention
This invention relates to a deflection yoke, mainly disposed in a color CRT comprising an in-line type electronic gun, in which a horizontal deflection magnetic field distorted in a pincushion and a vertical deflection magnetic field distorted in a barrel are generated.
2. Description of the Prior Art
In general, a deflection yoke disposed in a color CRT containing an in-line type electron gun comprises a horizontal deflection coil of the saddle type, and a vertical deflection coil of the toroidal type or saddle type. The horizontal deflection coil and the vertical deflection coil generate a horizontal deflection magnetic field distorted in a pincushion and a vertical deflection magnetic field distorted in a barrel, respectively. Therefore, the deflection yoke may have construction in which a dynamic convergence circuit is not required, that is, construction of a self-convergence. On the other hand, this kind of distorted magnetic field may become a cause for generating coma distortion. As shown in FIG. 3, in a picture with a convergence distortion, a green raster G due to an electron beam of the center and red and blue rasters R and B due to an electron beam of both sides are vertically shifted with each other. Also, as shown in FIG. 4, a rotational distortion (a spot distortion) can readily occur in red and blue beam spots which are formed from the electron beam of both sides at the periphery of the picture, and the generation of such a spot distortion makes it difficult to obtain high resolution tube performance.
As a solution to the above-mentioned problems, in the invention disclosed in the Japanese Laid-Open Patent Publication No. 62-217546, an electron gun section of a vertical deflection magnetic field is distorted in a pincushion. That is, first and second magnetic members pick up a leakage magnetic flux from a vertical deflection coil of the toroidal type, and a function of generating the magnetic field performed by both magnetic members generates an auxiliary magnetic field for correction in a pincushion distribution at the end portion of the electron gun.
The solution to coma distortion by the use of the above-mentioned construction is very effective. However, it is difficult to satisfactorily obtain a required auxiliary magnetic field in a pincushion distribution only by the first and second magnetic members. Actually, it is necessary to adjust the distribution of a coil winding of the vertical deflection coil itself. Moreover, when the distribution of the coil winding of the vertical deflection coil itself is adjusted as a part of the solution to the coma distortion, the adjustment capacity of the distribution of the coil winding for convergence correction is lowered.